Control of sowthistle and prickly lettuce is difficult in pulse crops in southern Australia due to a lack of available postemergence (POST) herbicide options and widespread resistance to acetolactate synthase (ALS) inhibitor herbicides. The introduction of new herbicide tolerance traits to these crops is one possible avenue for improving control options. This study evaluated control of ALS inhibitor-resistant sowthistle and prickly lettuce in a novel breeding line of metribuzin-tolerant lentil under development in an Australian lentil breeding program. Field experiments conducted over three site-years in South Australia evaluated different rates and application timings of metribuzin, with and without the addition of POST diflufenican, compared to pre-emergence terbuthylazine applications. Herbicide treatments achieved significant levels of control of both sowthistle and prickly lettuce compared to the untreated control, and there was no negative effect of these treatments on lentil establishment or yield, despite two sites experiencing environmental conditions conducive to crop damage by the herbicides used. Greater levels of weed control were observed at higher rates of metribuzin for post-sowing pre-emergence application timings (for prickly lettuce) and with the POST application of diflufenican. Terbuthylazine treatments also performed well compared to the untreated control; however, they were not as effective as the higher rates of metribuzin. These results indicate that the introduction of a metribuzin-tolerant lentil cultivar will provide an effective in-crop broadleaf weed control option whilst also avoiding some of the herbicide damage risks associated with currently available options.

Twenty-six cultivars of tomatoes from several countries were divided into four metribuzin [4-amino-6-tert-butyl-3-(methylthio)-1,2,4-triazin-5(4H)-one] tolerance groups: tolerant, semi-tolerant, semi-susceptible, and susceptible. Early maturity and tolerance to metribuzin were correlated (r = −0.78) in the field experiment and (r = −0.72) in a sinking leaf-disc bioassay. New super early cultivars were especially sensitive to metribuzin. Chlorophyll a and b content were not highly correlated with tolerance to metribuzin. Metribuzin rates used for weed control are close to toxic concentrations for very early cultivars of tomatoes. Plants in the 9-leaf stage were less sensitive than plants in the 5- or 7-leaf stage. Metribuzin tolerance came at later stages in early maturing cultivars than in later maturing cultivars.